Polymer-ceramic multilayer composites with high fracture toughness

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Two groups are working together in this research project and it is the aim to develop and understand the property-structure-relationships of tough layered composites consisting of polymer and ceramic layers. For this purpose, layered composites of adhesively bonded ceramic foils will be prepared. The innovative composites should have a stiffness and a strength on a similar level like the applied high-perfotmance ceramic but higher mechanical reliability and toughness. The composite properties should highly depend on strength and elongation at break of the used adhesives which will be varied systematically. Furthermore, the adhesives amount should be kept as low as possible. The adhesives will be based on cationically curing epoxy resins. In our previous work we found that the modification of epoxy resins with partially crystalline polyesterpolyols, mainly based on poly(caprolactone), improves fracture strength and elongation at break strongly. The combination is better than that of high end commercial adhesives although our materials are not systematically formulated. There are indications that the outstanding properties are mainly caused by a heterogeneous morphology of the polymerised adhesive, although they seem to be homogeneous on the macroscopic level. The structure of the poly(caprolactone) will be varied therefore systematically and these compounds will be applied then for the adhesives preparation. The selected polymer system is most sufficient for basic examinations as its properties can be adjusted by only minimal changes of the composition. If photochemical curing is applied at different temperatures, heterogeneity can be varied even with identical composition. This allows the separate examination of the influence of morphology and composition on the adhesives properties. Different layer thicknesses of the ceramic foils and adhesive layers will be examined in order to work out the influence of the adhesives and the ceramics materials as well as of the construction of the layered composite stacks on the composites mechanical properties. For this goal an extensive work program will be carried out covering the physical and mechanical characterisation of the ceramic materials, the newly developed thermosetting adhesive polymers and the prepared layered composites. A deep understanding of the relationship between the structural variations and the resulting polymer as well as properties of the composites is expected. Beside the experimental investigation specific material models will be generated and applied for numerical simulation. The crack growth at the polymer ceramics interphase will be in the special focus of the numerical calculations. Based on the numerical results, layered composites with optimised properties will be prepared. Comparison between the experimentally determined properties of the layered composites and the results of the FEM calculations will contribute to the verification of the developed structure property models.